Re: Avoid extra Sort nodes between WindowAggs when sorting can be reused

On Sat, Jul 28, 2018 at 4:12 AM, Alexander Kuzmenkov
<a.kuzmenkov@postgrespro.ru> wrote:
> Daniel,
>
> Thanks for the update.
>
>
> On 07/25/2018 01:37 AM, Daniel Gustafsson wrote:
>>
>>
>>> Hmm, this is missing the eqop fields of SortGroupClause. I haven't
>>> tested yet but does the similar degradation happen if two
>>> SortGroupCaluses have different eqop and the same other values?
>>
>> I wasn’t able to construct a case showing this, but I also think you’re
>> right.
>> Do you have an idea of a query that can trigger a regression?  The
>> attached
>> patch adds a stab at this, but I’m not sure if it’s the right approach.
>
>
> To trigger that, in your test example you could order by empno::int8 for one
> window, and by empno::int2 for another. But don't I think you have to
> compare eqop here, because if eqop differs, sortop will differ too. I
> removed the comparison from the patch. I also clarified (I hope) the
> comments, and did the optimization I mentioned earlier: using array instead
> of list for active clauses. Please see the attached v6. Otherwise I think
> the patch is good.
>

Thank you! That makes sense and the patch looks good to me. FWIW maybe
it's good idea to add the comment describing why we didn't that.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center